The present invention relates to a magnetic thin film, a method of manufacturing the magnetic thin film, and a magnetic head including the magnetic thin film, more precisely relates to a magnetic thin film, which is formed by plating and which has high saturation magnetic flux density and a low coercive force, a method of manufacturing the same, and a magnetic head including the same.
A schematic sectional view of a conventional magnetic head of a magnetic disk drive unit is shown in FIG. 2. A symbol 12 stands for an MR head; a symbol 10 stands for a lower shielding layer of the MR head 12; and a symbol 14 stands for an upper shielding layer 14 of the MR head 12. The upper shielding layer 14 acts as a lower magnetic pole of a write-head section.
The lower magnetic pole 14 has an end magnetic pole section 16, and a surface of the end magnetic pole section 16 is covered with a magnetic layer 17. An upper magnetic pole 18 is provided to face the lower magnetic pole 14. A magnetic thin film 19 covers an inner face of the upper magnetic pole 18 and faces the magnetic layer 17. A write-gap “A” is formed between the magnetic layer 17, which covers the end pole section 16 of the lower magnetic pole 14, and the magnetic thin film 19. Symbols 20 stand for coils.
In the magnetic head for high recording density, the narrow write-gap “A” is narrow, a width of a front end of a write head core is made as narrow as possible, saturation magnetic flux density “Bs” of a material of the write-head section is made as great as possible, and the material of the write-head section has soft magnetism or a small coercive force. If the coercive force of the material is great, current responsibility is low when the magnetic head is driven, so that recording characteristics are made worse. Especially, hysteresis loss, which causes problems in a high frequency band, is caused, so that the recording characteristics in the high frequency band are made worse.
As shown in FIG. 2, a front part of the upper magnetic pole 18 is bent like a step so as to concentrate fluxes to a front end of the write-head section, and its thickness is about 3–4 μm. Therefore, the magnetic pole is formed by a plating process, which has high eleposition efficiency and which is capable of highly selectively forming films.
Conventionally, the magnetic film (saturation magnetic flux density Bs≅1.5 T) of the magnetic pole of the write-head section is a 45 NiFe film formed with DC current. These days, magnetic films having greater saturation magnetic flux density are required with increasing recording density.
Many magnetic films are disclosed. For example, a plated film made of CoNiFe (see Japanese Patent Gazette No. 11-741227), a plated film made of NiFe (see Japanese Patent Gazette No. 2002-208109) and plated films made of CoFe (see Japanese Patent Gazettes No. 2002-280217, No. 2003-45719 and No. 2003-34891) are known.
In Japanese Patent Gazette No. 11-741227, the plated film made of CoNiFe has saturation magnetic flux density Bs≧2.0 T and good soft magnetism. However, stress of the plated film is great, so thickness of the plated film must be severe.
In Japanese Patent Gazette No. 2002-208109, the plated film made of NiFe has high saturation magnetic flux density Bs=1.9 T and high corrosion resistance. However, the saturation magnetic flux density do not reach that required now.
In the plated films disclosed in Japanese Patent Gazettes No. 2002-280217 and No. 2003-45719, Fe is employed as a main element so as to have higher saturation magnetic flux density. Japanese Patent Gazette No. 2002-280217 discloses a method of manufacturing the FeCo plated film having higher saturation magnetic flux density Bs=2.25-2.3 T. Japanese Patent Gazette No. 2003-45719 discloses the FeCo film, which includes a third noble metal element so as to improve corrosion resistance. The FeCo film has higher saturation magnetic flux density Bs=2.2 T and high corrosion resistance. However, coercive forces of the magnetic films disclosed in Japanese Patent Gazettes No. 2002-280217 and No. 2003-45719 are 1500 A/m or more, which is greater than conventional films having soft magnetism. Therefore, they make recording characteristics of magnetic heads worse.
Conventionally, the coercive force of a magnetic material is reduced by two ways. One is mixing impurities in a plated film so as to microcrystallize the plated film. The other is a heat treatment at high temperature. However, impurities should be removed from the FeCo film and the CoNiFe film for higher saturation magnetic flux density. And, the heat treatment for the write-head section is executed in a final process of manufacturing a magnetic head, so the heat treatment should be performed in a prescribed temperature range, in which a read-head section is not badly influenced. Therefore, it is difficult to manufacture the CoFe plated film having the higher aturation magnetic flux density and the small corcive force.
A base film is required so as to form the plated film. Composition and saturation magnetic flux density of the base film are almost equal to those of the plated film, and the base film is formed in a vacuum apparatus. For example, the base film having high saturation magnetic flux density is made of FeN, FeCo, FeCoO and FeCoA10. FeCoO and FeCoA10 have high specific resistance, e.g., about 100 μΩ cm, so thickness of the base film is apt to vary and they are not proper as materials of the base film. On the other hand, FeN and FeCo have high saturation magnetic flux density and low specific resistance, so they are proper materials of the base film. However, they have low corrosion resistance to acidic liquids, so that they are dissolved by plating solution.